As an independent flooring inspector, I have repeatedly stated how important it is to check the subfloor to gauge its moisture content. If you do not check it at the onset it may very well come back to haunt you.
Even floating floors:
Builders have a habit of underestimating moisture contents in floors, suggesting that a subfloor is dry enough to lay a wooden floor on with a simple vapour barrier because there is a damp proof membrane installed under the screed. However, as a flooring contractor, you must be strong and insist on carrying out a moisture test. If the RH reading is above the magical 75% then it is vital that an appropriate liquid damp proof membrane (See image below) is installed.
A sandwich damp proof membrane can also be used (See image no.3)
All too often, as a flooring inspector, I am called to look at failed or discolouring flooring (See image below).
99% of the time the failure of the floor is a result of high moisture content and usually coupled with an inadequate damp proof membrane.
As a professional independent flooring inspector, I urge all you contractors to be stronger and insist on installing a suitable D.P.M. Because, if you do not, the floor WILL fail and it will not only come back to haunt you but hurt your pocket.